The men kept a food diary each day of the study (seven days during baseline and 42 days during the low-carbohydrate diet) and the control group kept seven-day records during weeks one and six.

Here’s what daily nutrient intake looked like in both groups during the final week of the study.

Control group

Total calories 1,949 caloriesProtein 80 grams (16% of total calories)Carbohydrate 283 grams (58% of total calories)Fat 56 grams (26% of total calories)

Ketogenic diet group

Total calories 2,334 caloriesProtein 176 grams (30% of total calories)Carbohydrate 46 grams (8% of total calories)Fat 157 grams (62% of total calories)

And the result?

The men on the low-carbohydrate diet gained just over two pounds of muscle. The control group, on the other hand, gained just under one pound.

However, while the keto dieters gained twice as much muscle as the control group, this doesn’t necessarily mean that such a diet is the best way to pack on size.

The first problem is the big difference in protein intake between the two groups.

A closer look at the food records reveals that subjects on the ketogenic diet ate TWICE as much protein than those in the control group (176 grams versus 80 grams per day).

The extra muscle growth in the low-carbohydrate group was most likely down to the fact they were eating more protein.

This brings me to the subject of exercise.

In an ideal world, both groups would have followed the same training program. But that doesn’t appear to have happened in this study. The only information about the type of training routine used in the research was this:

“Subjects were moderately active performing a variety of different aerobic and weight-training routines, but none were competitive athletes. In the carbohydrate-restricted diet group, 1 subject was sedentary, 5 performed regular exercise (2 to 4 times per week for 20 to 60 minutes) and 6 performed a combination of aerobic exercise (3 to 5 times per week for 15 to 90 minutes) and resistance exercise (2 to 6 times per week for 45 to 120 minutes). Subjects were required to maintain their current level of physical activity during the study.”

What this means is that all subjects in the low-carbohydrate group were following a different exercise program, and we have no idea what sort of exercise the control group was doing.

In other words, any differences in muscle growth between the two groups could have been due to a better training program rather than diet alone.

More recently, a team of Florida researchers ran a similar study [9]. But this time, protein intake was matched between the two groups, and everyone in the study followed the same training program

A group of 25 college aged men, all of whom had been training for an average of 5.5 years, were divided into a ketogenic or traditional Western diet group.

The Western diet consisted of 20% calories from protein, 55% from carbohydrate, and 25% from fat. The keto dieters got 20% of their calories from protein, 5% from carbohydrate (including fiber), and 75% from fat.

Protein intake was matched at around 130 grams per day, and all subjects lifted weights three times per week for 11 weeks.

What happened?

From weeks 1-11, the keto group gained roughly twice as much lean mass as subjects on the standard Western diet. Gains in muscle thickness, measured using ultrasound, were also significantly greater in the keto group.

On the surface, this study appears to provide strong evidence that keto diets are the way to go if you want to build muscle.

But only until you take a closer look at the way it was done.

The keto group “carbed up” in the final week of the study, which led to a gain of 6.6 pounds (3 kilograms) of lean mass. In other words, much of the gain in lean tissue came from glycogen (the name given to carbohydrate stored in the body) and water.

If you look at the results from weeks 1-10, before the keto group bumped up their carb intake, there was no significant difference in the rate of muscle growth between the two groups.

Even the researchers write that it’s “likely that both groups gained similar amounts of muscle mass throughout the entire study.”

Doubts have also been raised about the independence of various researchers involved the study, as some of them had potential conflicts of interest that weren’t disclosed in the research paper.

The lab also has a reputation for publishing results that seem a little too good to be true, and other researchers have questioned the veracity of their previous findings on HMB and muscle growth [10].

Personally, I’ve seen no evidence to suggest that the results from this study have been tampered with. However, there are claims that the data used in the research is fraudulent. In any case, the whole thing sounds a bit fishy to me.

Will You Lose Less Muscle on a Ketogenic Diet?

When you’re trying to lose weight, it’s all too easy to end up losing muscle along with the fat.

One of the arguments in favor of the keto diet is that it has a “protein sparing” effect, which allows you to preserve more muscle during weight loss than if you hadn’t been ketogenic.

To put the idea to the test, a team of Brazilian researchers took a group of 21 overweight men and women, and got them to train with weights three times a week for eight weeks [11].

Half the subjects were told to restrict their carbohydrate intake to less than 30 grams per day during the first four weeks. Afterwards, they were allowed to add 10 grams of carbohydrate each week until the end of the study.

The other half followed a more conventional diet, where 55% of their calories came from carbohydrate, 15% from protein and 30% from fat.

Both groups ate a similar amount of protein – roughly 0.7 grams per pound (or 1.5 grams per kilogram) of bodyweight.

The result?

There was very little difference in results between the low carb and conventional diet groups. They both got stronger, lost fat, and reduced their waist size. There was also no significant difference in muscle growth – measured with ultrasound at the biceps, triceps and quadriceps – between the two groups.

To quote the researchers directly:

“The main result of this study was that, irrespective of carbohydrate content, the hypoenergetic diets did not impair strength gains, and the volunteers were able to maintain muscle thickness during resistance training. Furthermore, significant similar reductions were observed in body mass and body fat in both diet groups.”

Similar results were found in a 12-week study of 42 men with metabolic syndrome [12], and a 10-week study of overweight women [13].

Pairing resistance training with a ketogenic diet had no beneficial (or adverse) effects on the preservation of muscle mass during weight loss compared to the same training program paired with a conventional diet.

A six-week study of men and women doing CrossFit four times a week also fails to show that keto diets have any special muscle-building properties [14]. Subjects who went low carb gained no more muscle than a control group who were told to carry on eating their regular diet.

Keto Diets and Gymnasts

One study that’s often used in support of ketogenic diets looked at a group of elite male gymnasts during two 30-day periods [15].

For the first 30 days, the gymnasts followed a low-carbohydrate diet and continued with their regular training. They also performed a series of strength tests to see how well their performance held up.

Three months later, they switched to their normal diet, and went through the same battery of tests.

During both periods, the men could eat as much food as they wanted. However, during the keto phase of the study, they ended up eating 300 fewer calories each day.

As a result, they lost weight.

What’s more, all the lost weight (4 pounds or 1.9 kilograms) came from fat. There was also a small non-significant increase in muscle mass.

In other words, when they were on the keto diet, the men lost fat and gained a bit of muscle.

And, other than during the first couple of weeks, when the gymnasts complained that they couldn’t finish all the exercises, restricting carbs had no adverse effects on performance. They performed equally well on both the normal and low-carb diets.

What’s not to like?

When you dig into the study, there were several problems with the way it was done that limit the conclusions we can draw.

For one, there was a big difference in protein intake between the two diets.

During the low-carb phase of the study, the gymnasts averaged 201 grams of protein per day. That compares to just 84 grams during the normal diet. So, we don’t know if the benefits of the diet were down to the extra protein rather than the reduction in carbs.

Second, such a high level of protein has the potential to kick you out of ketosis. That’s because amino acids can be converted into glucose by the body. In fact, we don’t know if the gymnasts were in ketosis or not, as ketone levels weren’t measured in the study.

But that’s not all.

During the keto diet, the gymnasts took a supplement containing various herbal extracts. But they didn’t use the same supplement when they were on their normal diet.

What impact did the supplement have on the results?

We don’t know. But it could have skewed the results in favor of the low-carb group.

In short, there were several problems with the way this study was set up, and it’s a long way from the ringing endorsement for ketogenic diets that some like to claim.

Final Thoughts

To sum up, it is possible to gain muscle on a ketogenic diet.

What’s more, there are several studies out there to show that ketogenic diets do just as well as their higher carb counterparts when it comes to preserving muscle while you lose fat.

However, there’s currently no compelling evidence to show that ketogenic diets offer any muscle-building benefits that you don’t get with a higher-carb diet providing adequate amounts of protein and fat.

ABOUT CHRISTIAN FINN

Christian Finn holds a master's degree with distinction in exercise science, is a former personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Fit Pro, Zest, and Perfect Body magazine.